I live in usa wooded area near fast moving river. I've been bite several times over th past few years. I usually have a stream of blood left from where I've been bitten. It leaves a large red welt for about a week, sometimes a larger red patch around the bite. It leaves me wondering if these bites cause muscle soreness , headache and fatigue. I think I usually feel this way for days-weeks after a bite. I never see them when they get me. Almost always it's around hairline, face, neck or chest. The neck and chest bites seem to always bleed quite a bit,I find a trickle of dried blood several inches long from bite site, which soon after itches and is sore. I eventually baught a dark net (think it's called a bug baffler. I wear it with a basball cap under it to hold the net away from my face. It has elastic straps that go under the arms and hold the net (kinda) snug against the body. Over this I wear a white hooded sweatshirt that I have previously sprayed with deep woos repellent. I LOOK RIDICULOUS! But I can't go into my backyard without it. I think one bite is enough to make me sick with the muscle soreness, headache (days) and tiredness. I would cover yourself fully when entering your garden. It's hot but it keeps me unbitten!
forgive all the typ-o's and spelling error- figure you were in a hurry to hear from someone, it's only been 2 years! LOL. Maybe you'll check this and know you're not alone. Wish they would treat areas for ALL blood-sucking, disease carrying insects!
SCB Without knowing where you are it is difficult to help. You need to catch one or two to check that they really are blackflies. The same symptoms could be caused by even smaller (nearly invisible) culicoides sandflies or no-see-ums.
You seem to have developed a mild allergy to the bites. I suggest you contact your local mosquito abatement authority (assuming there is one) and see if they are active in your area. If enough people complain they might be forced to take action. Sorry I cant be more positive, in my experience repellents have very limited effectiveness so you seem to have found the best local solution.
Its been unseasonably warm few days. Flies have probably come out of hibernation, or have emerged from overwintering pupae. Do you usually have blackflies biting in the summer? Difficult to predict the future. E. Yorkshire is a pretty large area, can you be more specific as to where you are?